We are requesting funds for a Gammacell 40 Cs-137 irradiator able to irradiate tissue culture cells and whole animals. The irradiator is absolutely necessary to carry out the research mission of the Department of Radiation Oncology, the Massey Cancer Center and Virginia Commonwealth University, and the objectives of extramurally funded research projects in molecular radiobiology and medical physics. This is a dedicated research irradiator that will replace an old Co-60 unit, which will soon no longer be readily available for day-to-day irradiations. Furthermore, when our new cancer center is finished in the early part of 2006 there will be an increased demand for an irradiator in close proximity to laboratories and animal facilities after consolidating existing and new faculty to one location. The irradiator is important for basic and translational molecular radiobiology research that eventually may lead to improved treatments of cancer. [unreadable] [unreadable]